A little trick i learnt: The atomic number reflects how many electrons there are, and there must be an equal charge. therefore, there are the same amount of protons as there are electrons. so if it has 81 protons, we look for number 81 in the periodic table, Thallium
<span>The correct answer is A. atoms. Atoms are studied by physics and chemistry, not by ecology. Ecology studies organisms, populations, and the earth in terms of climate, pollution prevention, natural habitats and biomes, and all kinds of similar things that are related to living on earth. Atoms are irrelevant for the study of ecology.</span>
<span>They are reactions that complement each other in the environment.</span>
